The invention disclosed relates to a multi-purpose tube-nest evaporator, an item of apparatus intended specifically for use in the concentration of liquid foodstuffs (juices etc.), or of chemicals, but which might be used for any compatible purpose. The evaporators used in plant for implementing such a process will generally incorporate tube nest heat exchangers, the tubes of which are vertically disposed in most instances; the method by which a given product is fed through such an evaporator is dependent upon its degree of viscosity.
More precisely, significantly viscous fluids require forced circulation, whereas a less viscous product can be cascaded through the evaporator in a free-falling film, the advantages of which are considerable, namely: a high overall heat exchange coefficient; low power requirement as regards propulsion of the product through the tube nest; and faster throughput. Where a product is simply cascaded, in fact, the power rating of the pump installed can be drastically reduced in relation to that of a pump used to force-feed viscous products.
The requirement for an evaporation facility in which one or more stages can be utilized by turns to force-feed and cascade a product has led to the embodiment of evaporators in a multi-purpose type of design. In prior art embodiments, conversion of the evaporator to enable the switch from force-feed to cascade type operation involves, on the one hand, installation of a second pump with a capacity rating significantly lower than that of the pump utilized in force-feeding viscous products, and on the other, fitment to the inlet bulkhead of the tube nest of one or more baffles by means of which to control the flow of liquid.
The addition of such baffles to an existing evaporator is no simple matter; the baffles must be installed internally, and this necessitates shut-down of the system in order to carry out the necessary dismantling and re-assembly operations.
The main object of the invention is that of overcoming the drawback described above, namely, to effect conversion quickly from a force-feed type operation to a cascade operation without evaporator shut-down for baffle dismantling and reassembly operations. A further object of the invention is to provide a system that gives the facility of a quick and simple switch between the force-feed type of operation required for viscous products, and the cascade operation which enables exploitation of a free-falling film alternatively, within an evaporator.
One advantage of the invention is that the switch from one type of operation to the other can be effected automatically by way of means which may be operated from a control panel from the evaporator.